The present invention relates generally to a table saw fixture and particularly to a fixture and fixture combinations which provide accurate alignment to enable square cuts to be made on a workpiece. The invention also relates to a method of verifying the alignment of the arbor for the cutting blade, relative to the guide groove in the work supporting table of a table saw, as well as a method of and apparatus for adjusting the alignment of the arbor relative to the guide groove.
The modern table saw has a work supporting table which is provided with a slot and at least one guide groove in the upper surface of the table which is parallel with the slot. A circular cutting blade is mounted on an arbor which is rotatably mounted on a cradle which is connected to the table so that the blade extends through the slot in the table. The cradle is mounted on the table so that it can be raised or lowered and so that it can be rotated about a front to back horizontal axis. This enables the operator to adjust the amount of cutting height of the saw and the cutting angle of the saw, relative to the upper surface of the work supporting table.
The arbor supporting cradle in most modern table saws is pivotally mounted between a pair of trunnions. One trunnion is fastened to the bottom surface of the supporting table at the front end of the table saw. The other trunnion is fastened to the bottom surface of the supporting table at the rear end of the saw. The rear trunnion is fastened by bolts which extend through oversize holes in the rear trunnion. This enables the rear trunnion to be moved laterally a small amount, relative to the front trunnion, to correct for a possible misalignment of the arbor relative to the guide groove in the work supporting table. It is essential that the arbor be at a right angle to the guide groove so that the cutting blade is parallel with the guide groove of the supporting table. If the cutting blade is not parallel with the guide groove, the bolts which fasten the rear trunnion to the supporting table are loosened and the rear trunnion is forced into an adjusted position, for example by striking the trunnion with a hammer to move the rear trunnion laterally and to change the alignment of the cutting blade relative to the guide groove. This represents a crude and imprecise adjusting feature. It is extremely difficult to align the cutting blade relative to the guide groove with any degree of accuracy by the use of hammer blows. Also, even if an accurate alignment of the cutting blade is achieved, the achieved correct alignment can be lost when the bolts which hold the rear trunnion to the table are tightened.
The accurate cutting of a workpiece can be affected by factors other than the alignment of the cutting blade to the guide groove of the supporting table. These other factors include a cutting blade which may not be perfectly flat, an arbor which may not be perfectly straight and a guide groove which does not have a uniform width or is too wide for the guide bar of a fixture which is used for a cutting operation.
Verification devices have been developed for checking the alignment of the cutting blade with the guide groove of a table saw and for the flatness of the cutting blade. A typical verification device includes an elongated guide bar for slidable mounting in the guide slot of the work supporting table, a cross bar which is connected to the guide bar for supporting a gauge such as a feeler gauge which has a dial face, a dial and a plunger which is mounted on the gauge for axial movement relative to dial face and which is operatively connected to the dial. Although the gauge portion of the verification device is a very accurate instrument, inaccurate readings are obtained from the gauge due to a less than precise fit of the guide bar portion of the verification device within the guide groove and the lack of uniformity in the width of the groove. One prior art specification device utilizes a split bar which can be adjusted to fit into the guide slot by screws which are threaded into the bar. However, the device must be readjusted for another application. Also, prior art verification device which employ a dial gauge are limited in the ways that they can be used, due to the manner in which the dial gauge is mounted on the cross bar.
Inaccurate cutting of a workpiece occurs even if the longitudinal axis of the arbor is properly aligned with the guide groove and the guide bar of the fixture, such as a miter gauge, fits perfectly in a perfectly uniform guide groove. Inaccurate cuttings can occur if the arbor is not straight or if the cutting blade is not flat. If the arbor is straight and the guide bar of the fixture fits perfectly in the guide groove of the table saw, a misalignment of the arbor relative to the guide groove or a warp in the cutting blade can be detected by existing verification devices. However, there is no effective way to determine the straightness of the arbor without removing the arbor from the table saw or of making a proper adjustment of the arbor if one or more other variables which affect alignment are present. If there are errors or flaws in two or more variables, it is very difficult to verify and isolate the flaws and to correct them.
Proper alignment of the cutting blade and fixtures is particularly critical when the table saw is used for cutting very thin strips from a workpiece, i.e. for cutting veneer strips. For such thin pieces, uniformity of thickness is critical. Cutting accuracy must be maintained with low tolerance for error. Also, there is a lower limit to the width of strip which can be cut on a table saw by using conventional equipment and methods. Still further, precise cuts are extremely difficult to obtain on a conventional table saw, using conventional fixtures. These and other difficulties experienced with the prior art table saws, table saw fixtures, and method of using the fixtures with table saws have been obviated by the present invention.
It is, therefore, a principal object of the invention to provide a verification apparatus for checking all variables in a conventional table saw which contribute to alignment errors between the cutting blade and guide groove in the work supporting table of the table saw.
Another object of the invention is the provision of a method of checking and measuring all variables in a conventional table saw which contribute to alignment errors between the cutting blade and the guide groove in the work supporting table of the table saw.
A further object of the invention is the provision of an apparatus for and a method of positively and precisely aligning the arbor of a table saw relative to the guide groove in the work supporting table of the table saw.
It is another object of the invention to provide a self-adjusting guide bar for sliding in the guide groove of a table saw for use with a plurality of saw fixtures and which maintains a constant and precise relationship between the fixture and the cutting blade of the table saw.
A still further object of the invention is the provision of an alignment gauge which has improved precision and versatility.
It is a further object of the invention to provide a locating gauge for use in a table saw to enable narrow pieces to be cut from a workpiece with improved accuracy and uniformity.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts and steps set forth in the specification and covered by the claims appended hereto.